The present disclosure relates to pressure sensitive adhesives and more particularly to a water-based pressure sensitive adhesive (“PSA”) suitable for high performance applications.
The manufacture of pressure sensitive adhesive tapes is being shifted from organic solvent systems to aqueous latices in order to reduce air pollution and fire hazard, as well as eliminate the rising expense of organic solvents. Pressure sensitive adhesives for high performance application must meet or exceed diverse, often seemingly incompatible, criteria. Initially, the adhesive must coat well on silicone or other release sheets. The adhesive also must exhibit tenacious adherence to film face stock which may serve a masking function or may convey information, e.g., by its imprinting.
When the adhesive coated film face stock is removed from the release sheet, the adhesive must exhibit initial tack and peel performance when pressure-applied to a substrate. The substrate bearing the adhesively-bound film face stock may be subjected to a variety of manufacturing operations over time. Thermal cycling of the substrate is a condition to which high performance, pressure sensitive adhesives must be designed to confront. When the film face stock is removed from the substrate, removal must be clean, i.e. no visible trace of the adhesive should remain on the substrate. Heat aging of the film face stock/substrate laminate, however, tends to cause the adhesive to “build”, that is, the necessity to utilize excessive force to remove the film face stock. Thus, the adhesive should stick well initially, but not so well that its later removal is difficult. Then too, the adhesive must possess shelf life, viscosity, etc., making it compatible with existing coating and handling techniques utilized in the art.
More particularly, all emulsion polymers foam due to their surfactant content. Without the addition of defoaming/antifoaming agents, emulsion polymers would be difficult at best to process into useful form, such as, for example, forming a film on a substrate. Unfortunately, most defoamers lose their efficacy over time. Adding additional defoamer to the emulsion prior to application may be of limited value due to numerous side effects encountered. Furthermore, coating of the emulsion often requires high shear, which may be compromised by the late addition of additional defoamer.
It is to this problem that the present PSA composition is addressed.